Method for suppressing the escape of volatiles while pressure baking carbon articles



* 1'. znsfom I 3,504,065

WHILE March31, 19,70

METHOD FOR SUPPRESSING- THE ESCAPE- OF-VOLA'IILES PRESSURE BAKING.CARBON ARTICLES Original Filed Aug. 15, 1966 w. w M\ INVENTOR- THEODOREEDSTROM BY ATTORNEY United States Patent 3,504,065 METHOD FORSUPPRESSING THE ESCAPE 0F VOLATILES WHILE PRESSURE BAKING CARBONARTICLES Theodore Edstrom, Parkview, Ohio, assignor to Union CarbideCorporation, a corporation of New York Continuation of application Ser.No. 572,573, Aug. 15, 1966. This application May 1, 1969, Ser. No.824,361 Int. Cl. B29c 25/00; C01b 31/00 US. Cl. 26429 3 Claims ABSTRACTOF THE DISCLOSURE An improved method for making a formed carbon articleis provided. The method includes the simultaneous application of amechanical and pneumatic pressure while heating a carbonaceous charge toa carbonization temperature. The charge is initially provided with ahigh binder content which together with the use of a pneumatic pressurewhich suppresses the escape of volatiles from the charge enables astrong, highly dense article to be produced.

This application is a continuation of Ser. No. 573,573 filed Aug. 15,1966, now abandoned.

This invention relates to the production of carbon and graphite massesand more particularly to an improved process of pressure baking carbonarticles.

A recently developed pressure baking method for producing carbonarticles comprises confining, in a refractory lined mold, a mixture offinely divided carbonaceous particles with a fusible and carbonizablecarbonaceous binder susceptible of thermal decomposition, subjecting themixture within the mold to a high mechanical pressure of the order of4500 pounds per square inch to compress the same, and passing anelectrical current of about 500 amperes per square inch of compressedmixture in the mold to heat the mixture to a temperature at whichsubstantially complete carbonizing of the binder constituent occurs. Bymeans of this process, it is possible to produce in about eight minutescarbon articles which heretofore required a production time of eightweeks.

In the above-described process, pitch and certain other binder materialsproduce volatile substances which condense on the press, punches, andcold sections of the mold. Accumulation of such substances prevents orinterferes with proper operation of the equipment, and in an extremecase can occasion minor explosions.

A recent improvement in the above described process which overcomes thisparticular disadvantage and which enables the use of higher binderconcentrations is disclosed in US. Patent 2,965,931 wherein it is shownthat the evolution of condensible hydrocarbons can be substantiallyeliminated by adding finely divided sulfur to the mix blend to reactwith the pitch component, thereby causing the evolved gas to becomenon-condensible and yielding a higher percentage deposition of bondingcoke. However, in addition to the fact that sulfur in the pitch bondedmix creates gases which are toxic and which are corrosive, the use ofsulfur in certain carbon products is sometimes undesirable because theoperating properties of the product are affected. For example, in themanufacture of carbon brushes the presence of a bond resulting from cokewhich has been deposited in the presence of sulfur causes relativelyhigh friction during commutation.

The principal object of this invention therefore, is to provide a methodof pressure baking carbon articles whereby the evolution of condensiblehydrocarbons is substantially eliminated without the use of a sulfuradditive.

Another primary object of this invention is to provide a method ofpressure baking carbon articles whereby higher binder concentrations maybe employed without the use of a sulfur additive.

These and other objects of this invention will become apparent from thefollowing description, taken in conjunction with the accompanyingdrawing wherein FIGURE 1 is an apparatus which may be suitably employedin the process of the invention; and

FIGURE 2 is a schematic of an auxiliary pressure supply and controlsystem.

Broadly stated, the objects of the invention are accomplished by theapplication of a pneumatic pressure to a carbonaceous charge while thecharge is being subjected to heat and mechanical pressure. The pneumaticpressure is preferably applied by contacting the charge with a gas in asealed chamber. The gas suppresses the escape of hydrocarbon volatilesfrom the charge with the result that the hydrocarbons are retained in aliquid phase and are forced to coke during the carbonization process.Thus the presence of condensates on the pressing ram and other equipmentis eliminated. Furthermore, a greater carbon yield is achieved andhigher binder concentrations may be employed.

Any gas may be employed in the instant process which does not oxidizethe carbonaceous mix. Such gases include nitrogen, argon, helium, carbonmonoxide and the like.

The pneumatic pressure is preferably applied prior to the application ofthe mechanical pressure and then maintained thereafter. Furthermore, itmay be increased or decreased during operation as will be hereinafterfurther described. For best results, a pneumatic pressure of at least 10p.s.i. and as high as 2000 p.s.i. or greater is applied while amechanical pressure of about 500 to 4000 p.s.i. compresses thecarbonaceous charge. A pneumatic pressure of between 50 p.s.i. and 1000p.s.i. is preferred.

Referring to FIGURE 1, an apparatus 10 suitable for use in the processof the invention comprises a steel cylinder 12 which encloses a hightemperature ceramic liner 14 and a carbon liner 16. Adjacent the carbonliner 16 is a graphite mold 18. A carbonaceous charge 20 having beensurrounded by coke packing 22, is situated within the area defined bythe graphite mold 18. Mechanical pressure is applied through a graphiteram 24 which may also serve as an electrical conductor to supply currentto the charge 20. The apparatus is sealed by means of Teflon 1 gasket 26and asbestos seal ring 28 thereby preventing the escape of volatiles orgas. A gas inlet conduit 30 passes through a steel cover 32 and contactsthe chamber 34 by means of a passage 35 around the ram extension 36 andthe graphite ram 24.

In operation, a non-oxidizing gas is fed into the chamber 34 through thegas inlet conduit 30 by placing a gas feeding means at the opening 31 ofthe conduit. A pneumatic pressure is thereby applied to the carbonaceouscharge 20 and escape of hydrocarbon volatiles from the charge isprevented. Mechanical pressure is applied to charge through the ram 24while the charge is baked. Upon completion-of the process, the graphiteram is withdrawn and the nonoxidizing gas is permitted to escape throughinlet conduit 30 by means of valve 46 as illustrated in FIGURE 2.

It will be appreciated that the pneumatic pressure which is applied tothe charge will be dependent on the volume of the chamber 34, thequantity of gas which is fed into the chamber, and the temperature towhich the gas is subjected. Normal expansion of the gas during heatingwill, of course, increase the pneumatic pressure since the apparatus iscompletely sealed. However, the pressure may be maintained at a desiredvalue by releasing gas from the system during the process. This may bereadily accomplished by one skilled in the art through the use ofTefionregistered trademark of Du Pont Corporatiou a. plastic consistingof a tetrafiuoroethylene polymer.

3 4 valves and the like which could conveniently be attached M.P.). Onegroup of samples contained parts of binder to the system as illustratedin FIGURE 2. per hundred parts of coke flour and another group con-Referring now to FIGURE 2, a typical pressure supply tained parts perhundred. The accompanying Table I and control system comprises a gascontaining means'38, shows the baked density, strength, and resistivityof these samples compared to control samples (Tests No. 1 and acompressor 40 which places the gas under pressure, a

No. 4) which were not prepared under pneumatic prespressure regulatedby-pass valve 42 connected across the compressor 40, a pressure inletvalve 44, a pressure resure.

TABLE I I Applied Efiective Time Estimated Gas Pressure (p.s.i.)Apparent Flexural meeh. meeh, on fire, fin density, Resistivity,strength, pressure pressure 2 sec. temp., C. Inltial Maximum gmJce.ohm-inch p.s.i. p.s.i. p.s.1

45 l, 200 1 0 0 1. 565 0. 00299 1, 210 4, 000 4, 000 52 l, 400 0 500 l.569 0. 00242 1, 650 4, 000 4, 000-3, 500 46 1, 000 600 1, 000 1. 576 0.00224 1, 880 4, 000 3, 400-3, 000

1 0 denotes atmospheric pressure. 2 Applied mechanical pressure lesspneumatic pressure. lease valve 46 to insure safety and to control thepressure 0 Table I indicates that at the lower pitch concentration,

applied, pressure gauge 48 which measures the pneumatic used in tests 1,2, and 3, which is representative of a pressure at all times and gauges50, 52 which measure level near the maximum effectively employablewithout container pressure and line pressure: In operation this theapplication of pneumatic pressure, an increase in system is able toclosely regulate the pneumatic pressure fiexural strength and reductionin electrical resistivity to be applied to the charge by controlling thequantity of resulted with an application of a pneumatic pressure. Atgas, such as nitrogen which is supplied to the chamber 34. the higherbinder level, the end product made without Although a pressure supplyand control system such as pneumatic pressure (test 4) displays an evenlower apthat illustrated in FIGURE 2 is the preferred equipment parentdensity, and the specific electrical resistance is forapplyingapneumatic pressure, any manner of applicaeven higher, than theproduct made at 10 p.p.h. The tion is Within the concept of theinvention. For example, marked improvement in density and flexuralstrength a pneumatic pressure may be applied to the charge Withas wellas the lower resistivity obtained with the appliout the use of anexternal gas by simply sealing the apcation of pneumatic pressure at thehigher binder conparatus as hereinbefore illustrated. During heating,volacentration is evident from a comparison of test 4 results tiles willescape from the charge but not from the chamwith tho e obtained fromtests 5, 6, and 7.

ber 34. Since the escape of the volatiles from the apparatus isprevented, a pneumatic pressure is formed in EXAMPLE II the chamber asthe.vol.afiles Continue to "2 from? the In another test, a number of 2"diameter carbon plugs charge. At some point 1n the process, equtllbriumWlll he were made at 10 and 20 p.ph. Pitch levels from com agwmplbhedand no further ascape volanles from the ductive blend charges containinga somewhat coarser c .arge W111 Occur due.to the presure the Chamber Inpetroleum coke flour than that described in Example I. i mannerpneumatlc pressure pP l to the charge In this series of experiments allof the plugs were initially wlthou? the use of an external nonoxldlzlngIt be pressed at temperatures ranging from 700 C. to 900 C. appreciatedthat control of the pneumatic pressure is less and after removal fromthe pressure baking m old, were preclse .that achieved f i i of anexternal gas protectively packed in granulated coke flour and rebakedand m addition, some volatllrzation Wlll occur. However, in anelectrically heated furnace to 10000 C. to ensure by (lecrqasing Size ofthe.chambr equilibliumfis a uniform final temperature, after which thepermeability f F a relgnvely gf g g g g i gfg zfig g to gas flow of theinternal carbon structure of the plug 6 ecnve smce e escape o V a g wasmeasured. A set of permeability measurements was still sup stantiallysupprelssed. 31mm:1 i illiuzfrit g f gg made with the direction of gasflow oriented with the connec mg an escap" Va ve su as a y grain of thecarbon structure and another set with the numeral 46 in FIGURE dir tionf fl a ainst th rain i a ainst A number of tests evaluating theeffectiveness of the in- 2 gas g e g and with the direction ofapplication pressure by the vention were performed and are set forthbelow. Each of the tests was performed with apparatus and equipment El ii -t the fqltlowmg rlrable m t g' sim'lar to that illustrated in thedrawin en 5 15 6 PP e S mp e num ers earrng e 1 g subscripts A and W.The table also l1sts the apparent EXAMPLE I denslty and reststlvltyvalues obtained as well as the A series of 2" diameter by 2 /2" longcylindrical processing conditions.

TABLE II.GAS PERMEABILITY OF VARIOUS PRESSURE MOLDED CARBON SAMPLESProperties 1 Effective Processing, Binder Gas pressure, mech. press.Density, Admittance Sample No. level, p.p.h. start-end in mix, p.s.i.gm./ec. Res, ohm-cm. F (ml./sec.-em.)

10 0-0 4, 200 1. 613 00829 1207 1. 597 488 1755 10 500-500 4, 300 1. 62100940 0907 1. 611 620 1866 10 1, 000-1, 000 3, 800 1. 611 00870 1290 -1.608 652 1286 20 500-500 4, 700 1. 706 00574 0292 l. 702 505 0359 20Vacuum 1, 300 3, 900 1. 707 0300 1. 704 00540 0453 20 Vacuum 2, 500 5,200-2, 700 1. 718 00545 0097 start-end l. 724 300 0139 1 After rebakingto 1,000 C. samples were molded from a conductive carbonaceous It isevident from the data that the admittance of the blend charge ofpetroleum base calcined coke flour (55 plugs made from 20 p.p.h. bindermix with pneumatic Texas coke flour) and a coal tar pitch binder (175C., pressure applied during forming is lower by a factor of 6 to 20 ascompared with those made at a lower binder be appreciated that manyother forms of comminuted level. In addition to the lower permeabilityto gas flow carbon or graphite can be used in the practice of the thecarbon articles have a large increase in apparent deninvention. Forexample, such materials as pulverized sity and somewhat lower electricalresistivity. coal, artificial and natural graphites as well as lampblackand gas black in various proportions can be used to im- EXAMPLE HI 5part desired properties in the final carbon or graphite In anotherseries of experiments, samples of petroleum article. In addition, coaltars as Well as still higher coking coke flour mixes bonded in one casewith 105 melting value pitches may be employed as binders. For instancepoint pitch were heated in a mixer, extruded through a blend of graphiteflour and carbon black bonded with a conventional extrusion jumbo into1" diameter rods, high melting point pitch is found to be particularlyefcut into 3" lengths and then pressure baked to about 10 fective inobtaining articles having high apparent density. 850 C. in accordancewith the process of this invention. What is claimed is: In this seriesof pressure bakes the preformed green 1. In a process for making aformed carbon article plugs which were nonconductive were heated bypassage from a charge comprising carbonaceous particles and a of currentthrough the graphite mold liner rather than fusible carbonaceous binder,said binder tending to evolve by direct passage of current as was thecase with the substances which condense on the apparatus used in saidarticles described in the earlier examples. The extrusion process, saidprocess comprising providing a binder conmixes contained petroleum coke90 flour and pitch protent of greater than about 15% by weight of saidcarportioned in a weight ratio of 70 parts/ 30 parts. To this bonaceouscharge placing said charge in a mold, submix 4 parts of petroleum ba eummer oil a added jecting said charge within said mold to a mechanicalas an extrusion aid. pressure while simultaneously heating said chargeto a After removal from the pressure-bake apparatus the earhOIllZafieHtemperature, Sealing Said apparatus and carbon plugs were rebakedconventionally to 1000 C. during the application of Said mechanicalPressure P' and then to 3000 C. to convert them to graphite. Plugs p y aPilellhlatic Piessure higher than atmospheric whi h were extruded fro thsame mixes b t t pressure from an external source of a non-oxidizing gaspressure baked were also conventionally baked. A comto Said Chargewhereby the escape of Volatiles from Said parison of the apparentdensity obtained after extrusion Charge is substantially pp ed andwhereby an inand after the 1000 C. and 3000 C. baking step betweencrease in density and flexural strength is achieved in the thepressure-baked and conventionally baked plugs is formed carbon article.

shown in Table III. 3 2. The process of claim 1 wherein said pneumaticTABLE III 105 C. M.P. pitch binder, Pressure- 1000 C. baked A.D., 3000C. graph A.D., 800 C. coking value 1 Carbonization Conditions 2 GreenA.D., g./cc. gJcc. g./cc. binder Final Pneumatic Initial pneumaticApprox. Control, pressure, pressure, pressure, temp. Control, PressureControl, Pressure Control, Pressure Percent percent p.s.i.g. p.s.i.g. C.no press. applied no press. applied no press. applied carbon carbon 1500. M.P. pitch binder 1 Coking value represents the weight of carbondeposited by the pitch binder at high temperatures relative to theweight of the pitch originally used. 2 Estimated mechanical pressure wasapproximately 500 lbs./in.

The values shown under the 800 C. Coking value pressure is between about.20 pounds per square inch and column in the table show the markedincrease in perabout 2000 pounds per square inch. centage of carbonobtained from both kinds of pitch 3. The process of claim 1 wherein saidgas is nitrogen. when the plugs were baked under pneumatic pressure.

It should be pointed out that the greater convenience References Citedand more rapid processing ofiered by pre-forming by UNITED STATESPATENTS extrusion would not be possible except for the higher I binderlevels made usable by the application of pneu- 3 9/ 1961 Balaquer l854.7matic pressure during the rapid baking step. Low binder 3,246,056 966Shea et al 264-29 levels, not in excess of about 15% by weight of the3,249,964 5/ 966 Shaler 185 carbonaceous charge were found to berequired for rapid 3,336,424 3/1957 n y 26489 baking prior to theinvention. In the above described FOREIGN PATENTS experiment, chargeshaving a binder level of 30% were successfully processed. Chargescontaining only 15% 759,160 10/1956 Gr at Britain. binder would not beextrudable. Another advantage for 1 9/ 1961 G at Brita nthe pre-formingtechnique is elimination of the need 5 for applying high mechanicalpressures to the green JULIUS FROME Primary Examiner carbon during thebaking stage. As indicated, the me- JOHN M L Assistant Examiner chanicalpressures applied were never more than about 500 lbs./in. US. Cl. X.R.

While all of the examples described were limited to 7 2 64-93, 332 1 ithe use of petroleum coke flour-containing mixes it will

